Air screens



June 4, 1963 E. F. GYGAX 3,092,008

AIR SCREENS Filed Nov. 6, 1957 7 Sheets-Sheet 1 y ATT'K' E. F. GYGAX AIR SCREENS June 4, 1963 '7 Sheets-Sheet 2 Filed Nov. 6, 1957 //VI EN7'02 EE/VEJTF i YGAX E. F. GYGAX June 4, 1963 AIR SCREENS Filed Nov. 6, 1957 7 Sheets-Sheet I5 Q lNl EN Toe EmvssrF G YGA x I A rrrf June 4, 1963 7 Sheets-Sheet 6 Filed Nov. 6, 1957 mmm NNM

June 4, 1963 E. F. GYGAX 3,092,008

AIR SCREENS Filed Nov. 6, 1957 7 Sheets-Sheet 7 ZZZ INVENTOR 23a ERNEJTEGYGAX 5f ATTK 3,092,008 AIR SCREENS Ernest F. Gygax, Glendale, Mo., assignor, by mesne assignments, to Universal Match Corporation, Ferguson, Mo., a corporation of Delaware Filed Nov. 6, 1957, Ser. No. 694,805 11 Claims. (Cl. 98-36) This invention relates to improvements in air screens. More particularly, this invention relates to improvements in control mechanisms for air screens.

It is therefore an object of the present invention to provide an improved control mechanism for air screens.

It is frequently desirable to leave the doors of business establishments open during business hours and thereby permit free ingress and egress of patrons and potential patrons. At the same time, the doorways of those establishments must be equipped with devices that can keep dust, rain, snow and the like from entering those doorways, and that can keep the conditioned air in those establishments from being unduly affected by the outside air. One such device is disclosed in Ernst Steiner application Serial No. 465,680 for Device for Producing a Room- Closing Air Curtain, which was filed October 29, 1954 and which issued December 9, 1958 as Letters Patent No. 2,863,373; and that device directs a plurality of closelyspaced walls of air across a doorway to isolate the two areas at opposite sides of that doorway.

Steiners device normally directs the air walls through paths that are parallel to the doorway; but in the event United States Patent the air pressure at the external face of the air screen appreciably exceeds the air pressure at the internal face of that air screen, that device will incline those air walls outwardly. Also, Steiners device will increase the velocity of the air forming those air walls. The said device is intended to provide an infinite number of inclinations for the walls of air and to provide an infinite number of velocities for the air in those walls of air, thereby providing the exact inclination and velocity needed for each differential between the air pressures at the opposite faces of the air screen. When Steiners device is made sufficiently sensitive to provide the desired infinite number of inclinations and velocities, it tends to hunt; and when it is dampened sufficiently to avoid hunting. it is sluggish. The present invention largely eliminates hunting and yet provides prompt changing, of the inclination of the air walls and of the velocity of the air in those walls, by providing a control mechanism that supplies finite inclinations of the air walls and finite velocities for the air in those air walls. That control mechanism provides enough finite settings of the inclination of the air walls and provides enough finite settings of the velocity of the air in those air walls to stabilize the air screen and to prevent breakthroughs in that screen. It is therefore an object of the present invention to provide a control mechanism that can supply a finite number of inclinations of the air walls of an air screen and that can supply a finite number of velocities for the air in those Walls of air.

The control mechanism provided by the present inven tion makes it possible to adjust to the normal inclination of the air walls of the air screen with ease; and it does so by providing a variable resistor which determines the normal inclination of those air Walls. As a result, it is only necessary to adjust the setting of that resistor to attain the desired initial inclination of the air walls; and that adjustment is easily done. The resulting simple and easy adjustment of the initial inclination of the air walls is desirable. It is therefore an object of the present invention to provide a control mechanism for an air screen which has a variable resistor that regulates and determines the initial inclination of the air walls of that air screen.

3,092,008 Patented June 4, 1963 The control mechanism provided by the present invention also makes it possible to adjust the various finite inclinations of the air walls of the air screen with ease; and it does so by providing variable resistors that determine those finite inclinations. Consequently, it is only necessary to adjust the settings of the variable resistors to adjust the finite inclinations of the air walls of the air screen.

The variable resistors of the control mechanism provided by the present invention are connected to a Modutrol motor manufactured by the Minneapolis-Honeywell Regulator Company; and those resistors coact with resistors within that motor to constitute a balanced resistance bridge. By interconnecting those variable resistors to the resistors of that motor in different ways, it is possible to unbalance that bridge and cause the motor shaft to rotate to dilferent positions to re-balance that bridge. In so rotating, that motor shaft changes the inclination of the air walls of the air screen.

The control mechanism of the present invention provides an additional adjustment in the initial inclination of the air walls of the air screen; that adjustment including a variable length connecting rod between the crank arm on the motor shaft and a crank arm for the guide members of the device which produces the air screen. Further, that crank arm can be set in diiferent positions on the motor shaft. The overall result is that precise and easy adjustment of the initial inclinations of the air Walls is provided by the present invention.

The control mechanism provided by the present invention causes the velocity of the air in the air walls of the air screen to increase as the inclination of those air walls increases, and causes the velocity of that air to decrease as that inclination decreases. Furthermore, that control mechanism makes it possible to change the velocity which the air will have when the air walls are set at their smallest inclination.

The present invention varies the velocity of the air in the air walls by interconnecting the Modutrol motor with a variable voltage transformer which controls an electrically operated clutch between the shaft of the blower motor and the shaft of the blower. Whenever the shaft of the Modutrol motor rotates it varies the output voltage of the transformer and thereby causes the clutch to vary the slip between the shaft of the blower motor and the shaft of the blower. It is therefore an object of the present invention to interconnect a Modutrol motor with a variable voltage transformer, that controls a clutch between the shaft of the blower motor and the shaft of the blower, so rotation of the Modutrol motor shaft varies the output voltage of the transformer.

It is desirable to be able to adjust the output voltage of the transformer without changing the position of the shaft of the Modutrol motor. Such an adjustment is made possible by providing a crank arm for the variable voltage transformer which can be set at different angles relative to the rotatable shaft of that transformer, and so by pro viding an adjustable linkage between that crank arm and the crank arm of the Modutrol motor. It is therefore an object of the present invention to provide a crank arm for a variable voltage transformer which can be set at different positions relative to the shaft of that transformer and to provide an adjustable linkage between that crank arm and the crank arm of a Modutrol motor.

One embodiment of the present invention utilizes an inclined passageway for an electrically conductive liquid, and disposes electrically conductive probes in that passageway so they can be contacted by the electrically conductive liquid. The opposite ends of that passageway are connected to sensitive, flexible diaphragms, and those diaphragms flex in response to differentials between the air pressures at the internal and external faces of the air screen. Those diaphragms seal off, from the ambient atmospheres, the electrically conductive liquid in the passageway and also seal ofi the quantities of air between the opposite ends of that electrically conductive liquid and the inner faces of those diaphragms. In doing so, those'diaphragrns assure a full response of the electrically conductive liquid to differentials between the air pressures at the exterior faces of those diaphragms, while preventing contamination or dilution of the electrically conductive liquid because of the entry of moisture-laden or contaminated air. Further, those diaphragms prevent the loss of electrically conductive liquid through evaporation. It is therefore an object of the present invention to provide an inclined passageway for an electrically conductive liquid and to isolate the opposite ends of that passageway from the ambient atmospheres by sensitive, flexible diaphra'grns.

The electrically conductive probes in the inclined passageway will be selectively engaged by the electrically conductive liquid, and those probes will interconnect the variable resistors in difierent Ways to unbalance the resistance bridge. In this way, the dilferentials between the air pressure at the opposite faces of the air screen can unbalance the resistance bridge and thereby cause rotation of the shaft of the Modutrol motor.

Another embodiment of the present invention has a number of vertically adjustable probes and has a vertically movable container with an electrically conductive liquid therein. The probes are set at different levels, and the container moves up and down in response to variations in pressure. In doing so, that container selectively connects various combinations of the probes to the variable resistors to unbalance the resistance bridge and thereby causes the Modutrol motor to rotate its shaft. The cont ainer is light in weight and is readily moved, and consequently it gives prompt and accurate control of the Modutrol motor.

Other and further objects and advantages of the present invention should become apparent from an examination of the drawing and accompanying description.

In the drawing and accompanying description two preferred embodiments of the present invention are shown and described but it is to be understood that the drawing and accompanying description are for the purpose of illustration only and do not limit the invention and that the invention will be defined by the appended claims.

In the drawing,

FIG. 1 is a plan view of part of a device that forms a plurality of walls of air and directs them across a doorway,

FIG. 2 is a front elevational view of the part of the device shown in FIG. 1,

FIG. 3 is a front elevational view, on an enlarged scale, of an adjustable connector between the crank arm of a variable voltage transformer and a connecting rod,

FIG. 4 is a sectional view, on said enlarged scale, that is taken along the plane indicated by the line 4-4 in FIG. 3,

FIG. 5 is a sectional view, on said enlarged scale, that is taken along the plane indicated by the line 5-5 in FIG. 4,

FIG. 6 is a partially sectioned view, on said enlarged scale, of a crank arm and bracket for a Modutrol motor,

FIG. 7 is a circuit diagram of one embodiment of the control mechanism provided by the present invention,

FIG. 8 is a simplified schematic diagram of the resistance bridge provided by the control mechanism shown in FIG. 7, and it shows that bridge after the electrically conductive liquid has been moved out of engagement with the probes in the inclined passageway of FIG. 7.

FIG. 9 is a simplified schematic diagram of part of the resistance bridge provided by the control mechanism shown in FIG. 7, and it shows that bridge after the electrically conductive liquid has engaged the lowermost of the probes,

FIG. 10 is a simplified schematic diagram comparable to the diagram in FIG. 9, and it shows the bridge after 4 the electrically conductive fluid has engaged the second lowermost probe,

FIG. 11 is a simplified schematic diagram comparable to the diagram shown in FIG. 9, and it shows the bridge after the electrically conductive fluid has engaged the uppermost of the probes,

FIG. 12. is a plan view of another embodiment of the control mechanism provided by the present invention,

FIG. 13 is a sectional view of the embodiment shown in FIG. 12, and it is taken along the broken plane indicated by the line 13 13 in FIG. 12,

FIG. 14 is a schematic diagram of the electrical components of the control mechanism of FIGS. 12 and 13,

FIG. 15 is an end view of a pick up that connects the control mechanism of FIGS. 12 and 13 to an atmosphere adjacent the air screen,

FIG. 16 is a sectional view through the pick up of FIG. 15, and

FIG. 17 is a simplified schematic diagram showing the circuits of one of the control mechanisms provided by the present invention.

Referring to the drawing in detail, the numeral 30 denotes an angle iron that constitutes part of a frame to support the structure which forms and guides the walls of air that constitute the air screen. A second angle iron 32 is set at right angles to the angle iron 39, and one end of the angle iron 30 is welded to the vertical portion of the angle iron 32. A third angle iron 33 is set parallel to the angle iron 32, and the other end of the angle iron 30 is welded to the vertical portion of the angle iron 33. Still another angle iron, not shown, is set parallel to the angle iron 30, and it has its ends Welded to the vertical portions at the other ends of angle irons 32 and 33. The four angle irons constitute a rugged and sutrdy supporting frame; and, in the particular device shown, those angle irons define a horizontal frame.

The numeral 34 denotes guide members which are elongated, which are generally triangular in cross section, and which are hollow. The guide members 34 are secured to .the angle irons 32 and 33 by pivots 36 and 38; and those pivots confine the guide members for rotation about horizontal axes that are parallel to the angle iron 3t). A connecting rod 4t} is suitably pivoted to each guide member 34, and consequently that connecting rod causes those guide members to rotate simultaneously about the pivots 36 and 38.

An elongated arm 42 is secured to one of the guide mebers 34, as shown particularly in FIGS. 1 and 2; and that arm has a ball-receiving socket 43 secured to the upper end thereof by a nut 44. That socket holds the ball of a ball-equipped, perforated connector 45. A C- shaped clamp 47 is carried by the ball-equipped connector, and a nut 49 secures that clamp to that connector. The ball-receiving socket 43, the ball-equipped connector 45 and the clamp 47 are commercially available articles and are not, per se, part of the present invention.

The numeral 46 denotes a wall that is U-shaped in plan and that has the web thereof welded to the vertical portion of the angle iron 30. The lower edges of the flanges of wall 46 are welded to the horizontal portion of the angle iron 30. The wall 46 extends vertically upwardly above the level of the tops of the guide members 34. A horizontal plate 48 is suitably secured to the wall 46, as by welding that plate to the web of wall 46. A second horizontal plate 50 is secured to the wall 46, as by being welded to the web of that wall. A second vertically directed wall 52 is welded to one of the flanges of wall 46 and is therefore perpendicular to the web of that wall.

The numeral 54 denotes a Type M904E75 DS Modutrol motor manufactured by the Minneapolis-Honeywell Regulator Company. That motor has a shaft with both ends thereof squared off. The base of the motor 54 abuts the left-hand edges of the horizontal walls 48 and 50, and screws 56 extend through openings in that base and seat in those walls.

The numeral denotes a U-shaped bracket which has a pair of aligned square holes that neatly telescope over one of the squared-off ends of the shaft of motor 54. That bracket also has an unthreaded hole in one of the arms thereof and has an internally threaded hole in the other arm thereof; and those openings are in alignment and can accommodate a screw 62. The U-shaped bracket 53 telescopes over an elongated bracket 60 which is provided with an elongated slot, with a shaft-receiving opening and with live small openings that define an arc. The shaft-receiving opening in bracket 60 telescopes over the said one end of the shaft of motor 54; and any one of the five small openings in that bracket can be placed in register with the aligned holes in the arms of bracket 58. The screw 62 can then be passed through the unthreaded opening in one arm of the bracket 55, through one of the five openings in bracket 60, and then seated in the threaded opening in the other arm of bracket 58. The screw 62 will coact with the said end of the shaft of motor '54 to cause the brackets 58 and 69 to rotate with that shaft as a unit. The bracket 58, the bracket 66, and the screw 62 are standard equipment of the motor 54 and are not, per se, part of the present invention. A screw 63 seats in a threaded socket in the said end of the shaft of motor 54 to engage a washer that maintains the brackets 58 and 6t in assembled relation with that shaft.

The numeral 64- denotes a ball-receiving socket identical to the ball-receiving socket 43; and the socket 64 is mounted in the slot of the elongated bracket of). That socket can be set at any desired position along the length of the slot in bracket 6d, and can be held there by tightening up the screw 65. The socket 64 receives a ball-equipped periorated connector 67 identical to the connector 45, a G-shaped clamp 69, identical to the clamp 47, is carried by the connector 67, and a nut 71 secures that clamp to that connector. I

An elongated connecting rod 66 extends through th openings in the connectors 45 and 67 and is tightly secured to those connectors by the clamps 47 and 69. By setting the bracket 58 on the said one end of the shaft of motor 54 in the proper position, by setting the socket 6d at the proper distance along the length of the slot in bracket 69, and by properly spacing the connectors 45 and 67 on the connecting rod 66, it is possible to attain the desired amount of rotation of the guide members 34. It will usually be desirable to rotate the guide members 34 through forty-five degrees from their innermost position to their outermost position.

The numeral 68 denotes a U-shaped bracket which is identical to the U-shaped bracket 58, and the numeral 7a denotes an elongated bracket which is identical to the elongated bracket 60. The bracket 68 and the bracket '76 are secured together by a screw 72 identical to the screw 62; and those brackets are secured to the opposite end of the squared off shaft of motor 54 by a screw 73. A ball-receiving socket, not shown but identical to the sockets 43 and 64, is secured within the slot of bracket 7t A connector, not shown but identical to the connectors 45 and 67, is carried by the said socket; and that connector has a clamp 74 secured to it by a nut 75.

The numeral 76 denotes a Type 116 Powerstat manufactured by The Superior Electric C0., and that device is a continuously tapped auto-transforrner. The rotatable shaft of that Powerstat has a slot in the end thereof which can accommodate the blade of a screw driver. The numeral '78 denotes a bracket which has an elongated slot therein, and which has a hub that can be secured to the shaft of the Powerstat '76 by means of a set screw. By loosening the said set screw, by inserting the blade of a screw driver in the slotted end of the shaft of Powerstat 76, and by manually rotating the bracket 78, it is possible to set that bracket '78 at any desired position relative to the shaft of that Powerstat.

A ball receiving socket 79', identical to the sockets 43 and 64 is held in the slot of bracket 78 by a nut 80. The

socket 79 holds a ball-equipped perforated connector 81 identical to connectors 45 and 67; and a clamp 83, identical to clamps 47, 69 and '74, is secured to that connector by a nut 85.

The clamps 83 and 74 engage and hold a connecting rod b2; but the positions of those clamps can easily be adjusted relative to the connecting rod 82. Further, the positions of those clamps with regard to the brackets 7t) and 78 can easily be adjusted. This arrangement makes it possible for rotation of the shaft of motor 54 to provide the desired rotation of the shaft of the Powerstat 76. The motor 54 is provided with limit switches, not shown, that restrict the rotation of the shaft of that motor to one hundred and sixty degrees in each direction. The extent to which the shaft of Powerstat 76 must be rotated can vary considerably from the said one hundred and sixty degrees; and the adjustability of the ball-receiving sockets relative to the brackets '74} and 78 plus the adjustability of the clamps 74 and 83 relative to the connecting rod 82 make it possible to rotate the shaft of Powerstat 76 through a lesser number of degrees than the number of degrees through which the shaft of motor 54 is rotated.

The numeral 92 denotes an inclined passageway which is formed in an insulating block, not shown; and a vertical passageway 94 is provided at the upper end of the passageway 92. while a vertical passageway 96 is provided at the lower end of the passageway 92. The said block and the said passageways 92, 9d and 96 are parts of a commercially available device which is known as a Dwyer Air Filter Gage and which is made by the F. W. Dwyer Mfg. Co.

A tube 98 is secured to the said block adjacent the upper end of the vertical passageway 94, and a tube 100 is secured to the said block adjacent the upper end of the vertical passageway 96. The tubes 9% and 1% extend to housings i112 and 118, respectively, and thereby place those housings in communication with the passageways 92, 94 and 96. The housing 1&2 has two generally spherical walls that clamp a thin, readily flexible diaphragm 114 between them. That diaphram will preferably be a very thin rubber diaphragm; and that diaphragm will normally be under very little tension. The area of the diaphragm in housing 112 is quite large so a small pressure applied to that diaphragm will cause appreciable movement of that diaphragm.

The numeral 118 denotes a housing which is similar to the housing 112; and the two generally spherical walls of housing 118 clamp a diaphragm 12! between them. One face of each of the diaphragms 114 and 126 is connected to the inclinedpassage 92 in the block; and the other faces of those diaphragms are exposed to the atmospheres at the opposite faces of the air screen. In particular, the other face of the diaphragm 1 14 is exposed to the atmosphere at the outer face of the air screen while the other face of the diaphragm is exposed to the atmosphere at the inner face of the air screen.

The numeral 162 denotes a probe of electrically conductive material which is made in the form of a pin and which communicates with the inclined passageway 92. The numerals 1G4, 106 and 108 denote similar probes that also communicate with the inclined passageway 92. The various probes are spaced along the length of the inclined passageway 92, and they are selectively connectible together by an electrically conductive liquid within that passageway. While a number of different electrically conductive liquids could be used, one very useful liquid consists of one tenth of an ounce of copper sulfate in two ounces of water. That liquid is introduced into either of the vertical passageways 94- or 96 by removing the appropriate tube and using an eye dropper to introduce that liquid. Enough liquid should is intro duced into the passageway 92 to enable one end of the liquid in that passageway to be intermediate the probes 102 and 164 when the air pressures at the other faces of diaphragms 114 and 120 are equal.

a When the air pressure at the other face of the diaphragm 114 exceeds the air pressure at the other face of the diaphragm 120, the conductive liquid will move to the right in the inclined passageway 92; and, depending upon the extent of the unbalance in pressure, that liquid can move out of engagement with the probe 104 or can move out of engagement with both the probes 104 and 106. The large area of the diaphragms 114 and 120, the high degree of flexibility of those diaphragms, and the shallow inclination of passageway 92 enables a pressure differential of one-eighth of an inch water gage to move the liquid in the passageway 92 a distance of onequarter of an inch.

The numeral 124 denotes a potentiometer, and the numerals 126 and 128 denote two additional otentiometers. While separate potentiometers can be used, an elongated wire-wound resistor with adjustable taps will usually be used. That resistor will have three adjustable taps corresponding to the variable contacts of the potentiometers 124, 126 and 128, and will also have a fixed tap corresponding to the junction 130. The variable contacts of the potentiometers 124, 126 and 123 or the adjustable taps of the elongated wire-wound resistor are set by hand, as desired; but once those contacts or taps have been set, they will not be moved during the normal operation of the control mechanism provided by the present invention.

The numeral 132 generally denotes a Type 13DJ3 electronic relay manufactured by the Photoswitch Division of Electronics Corporation of America. The relay 132 is provided with a transformer, not shown, at least one capacitor, not shown, a vacuum tube, not shown, and an electromagnetic relay, not shown, with two normally closed sets of contacts 154 and 156 and with two normally open sets of contacts 158 and 160. That relay is also provided with fifteen terminals, but some of those terminals are not used in the circuit of the control mechanism provided by the present invention and are thus not shown in FIG. 7. The terminals which are used in the circuit of the control mechanism provided by the present invention are indicated by circles. The terminal 9 on relay 132 is denoted by the numeral 134, the terminal 6 is denoted by the numeral 136, the terminal 8 is denoted by the numeral 138, the terminal is denoted by the numeral 140, the terminal 2 is denoted by the numeral 142, the terminal 7 is denoted by the numeral 148, the terminal 4 is denoted by the numeral 150, and the terminal 1 is denoted by the numeral 152. The terminals E and F of relay 132 are denoted by the numerals 144 and 146, respectively. The normally closed contacts 154 are provided between the terminals 134 and 138, the normally closed contacts 156 are provided between the terminals 136 and 140, the normally open contacts 158 are provided between the terminals 133 and 148, and the normally open contacts 160 are provided between the terminals 140 and 150.

The numeral 161 generally denotes another electronic relay that is identical to the relay 132. Terminal 9 of relay 161 is denoted by numeral 162, terminal 6 by numoral 164, terminal 8 by numeral 166, terminal 5 by numeral 168, terminal 2 by numeral 170, terminal 7 by numeral 176, terminal 4 by numeral 178, and terminal 1 by numeral 180. In addition, the terminals E and F of relay 161 are denoted by the numerals 172 and 174, respectively. Normally closed contacts 182 are provided between terminals 162 and 166, normally closed contacts 184 are provided between terminals 164 and 168, normally open contacts 186 are provided between terminals 166 and 176, and normally open contacts 188 are provided between terminals 168 and 178.

As long as the terminals 144 and 146 of relay 132 are not connected together, and as long as the terminals 172 and 174 of relay 161 are not connected together, the contacts 154, 156, 158, 160, 182, 184, 186 and 188 will be in the positions shown. However, if the terminals 144 and 146 of relay 132 are connected together, the normally closed contacts 154 and 156 will open and the normally open contacts 158 and 160 will close; and those contacts will remain in shifted position as long as the terminals 144 and 146 are connected together. Similarly, the contacts of relay 161 will shift position when the terminals 172 and 174 are connected together and will remain shifted as long as those terminals are connected together; those contacts automatically returning to their initial positions when the oonection between terminals 172 and 174 is broken.

The numeral 196 denotes a lead which extends between the probe 168 and the terminal 146 of relay 132. A junction 191 is provided between the lead 190 and a lead 192 which is connected to the terminal 174 of relay 161. The numeral 194 denotes a lead which extends. between the probe 166 and the terminal 162 of relay 161. A lead 196 extends between the probe 104 and the terminal 172 of relay 161. A lead 198 extends between the probe 162 and the terminal 144 of relay 132. Terminal 144 of relay 132 is connected to terminal 166 of relay 161 by a lead 200; and terminal 148 of relay 132 is connected to the movable contact of the potentiometer 124 by a lead 202. A lead 204 extends between the movable con-tact of the potentiometer 124 and the lower fixed contact of a singlepole double-throw switch 206. A second single-pole double-throw switch is denoted by the numeral 208, and the two switches 206 and 2118 are ganged for simultaneous actuation.

A lead 210 extends between the terminal 150 of relay 132 and the junction between the potentiometers 126 and 128. A lead 212 extends between the terminal 134 of relay 132 and the movable contact of the potentiometer 126. Lead 214 extends between the terminal 136 of relay 132 and the movable contact of potentiometer 128. A junction 215 is provided in the lead 214, and a lead 216 extends between the junction 215 and the movable contact of the switch 208.

The numeral 218 denotes a lead that extends between the terminal 138 of relay 132 and terminal 178 of relay 161. A lead 220 extends between the terminal of relay 132 and terminal 164 of relay 161. A lead 221 extends between the movable contact of a potentiometer 222 and the terminal 168 of relay 161.

The numeral 224 denotes a step-down transformer which has its primary winding connected to a source of one hundred and fifteen volt alternating current by leads 226. A junction 228 is provided in one of these leads and a junction 230 is provided in the other of those leads. The secondary of the step-down transformer 224 provides twenty five volts, nad that secondary winding is connected to the motor 54.

A full wave rectifier 232 is connected to the output of the Powerstat 76. That rectifier will preferably be of the .dry disc type.

The numeral 234 denotes a three phase motor which is connected to a source of three phase, two hundred and thirty volt alternating current by leads 236. The motor 234 is provided with a clutch housing 238 which contains a magnetic clutch. That magnetic clutch is disposed between the output shaft, not shown, of the motor 234 and the output shaft 240 of the clutch housing 238; and it will determine the ratio of the speed of the motor output shaft to the speed of the output shaft 240. That ratio ranges from one to one to two to one. The motor 234, the clutch housing 238, the output shafit 249 and the magnetic clutch, not shown, within housing 238 are commercially available; constituting the Ajusto-Spede device of The Louis Allis Company. The output shaft 240 is connected to the blower, not shown, which moves the air that forms the air Walls of the air screen.

The magnetic clutch in the housing 238 is connected to the output of the full wave rectifier 232 by leads 242.

r A lead 244 extends between the junction 228 and the 9 terminal 152 of relay 132. A lead 246 extends between the junction 230 and the terminal 142 of relay 132. A juncture 247 is provided in the lead 246, and that junction is connected to the terminal 171 of relay 161 by lead 248. A junction 249 is provided in the lead 244 and that junction is connected to the terminal 181} of relay 161 by the lead 2511.

Referring to FIG. 8, the numeral 261 denotes the coil of a balancing relay within the motor 54; and that relay also has a coil 262. The coils 260 and 262 selectively attract the arms of a U-shaped armature 264 within the motor 54. A movable contact 266 is carried by the armature 264, and that contact selectively engages fixed contacts 268 and 270 of the balancing relay. Fixed contact 268 is connected to one end of motor Winding 272, and fixed contact 2711 is connected to one end of the other motor winding 274. One of the motor windings drives motor 54 in'the forward direction while the other of those windings drives that motor in the reverse direc tion. The other ends of windings 272 and 274 are connected together. A condenser 276 is connected across the cont-acts 268 and 274) to minimize arcing between those contacts and movable cont act 266.

The numeral 273 denotes a potentiometer that is part of the motor 54, and the movable contact of that potentiometer moves when the shaft of that motor rotates. The numeral 280 denotes the leads which extend between the secondary winding of transformer 224 and terminals 286 and 288 of th motor 54. A lead 282 extends between the terminal 2&6 of motor 54 and the junction of windings 272 and 274, and that lead is an internal lead of the motor. An internal lead 281 extends between terminals 286 and can of motor 54, an internal lead 283 extends between terminal 288 and the movable contact 266, while internal lead 285 extends between the terminal 288 and the movable contact of potentiometer 27 3. The remaining terminals of motor 54 are denoted by the numerals 214 and 29s; and terminal 2134 is connected to the movable contact of switch 2116 by a lead 298, while terminal 296 is connected to the lower fixed contact of switch 208 by a lead 3%.

As shown in FIG. 8, the wiring and elements below the level of terminals 2%, 294 and 296 constitute, with the exception of leads 2813, internal elements and connections within the motor 54. The elements and wiring above the level of terminals 291?, 294 and 296 constitute, with the exception of the element 392, elements and wiring external of the motor 54. The element 302 sybolically represents the connections which relay 132 individually, relay 161 individually or those relays jointly make between terminal 2% and potentiometers 124, 126 and 128 and junction 1311.

As shown in FIG. 17, each of the electronic relays 132 and 161 has the coil thereof connected as the plate load of the electronic tube thereof. Thus the coil 450 of the electronic relay 132 is connected as the plate load of the triode 452, and the coil 470 of the electronic relay 161 is connected as the plate load of the triode 472. A resistor 454 and a source 456 or" negative biasing voltage are connected intermediate the grid and the cathode of the triode 452, and that source of negative biasing voltage normally biases that 'triode beyond cut-off. A resistor 47 4 and a source 476 of negative biasing voltage are connected intermediate the grid and the cathode of the triode 472, and that source of negative biasing voltage normally biases that tn'ode beyond cut-off. The grid of the triode 45 2 is connected to the terminal 144 in FIG. 7 and is thus connected to the probe 162, the grid of the triode 472 is connected to the terminal 172 in FIG. 7 and is thus connected to the probe 104, the terminal 166 is connected to the terminal 144 and thus to the grid of the ltriode 452, the cathode of triode 452 is connected to the probe 108 via terminal 146, junction 191 and conductor 190, and the cathode of triode 472 also is connected to the probe 1% via'terminal 174, condfuctor 192,

, 1h junction 191 and conductor 1%. When the liquid in the passageway 92 simultaneously engages the probes 106 and 108, the conductor 2%, terminal 166, normally-closed contacts 182, terminal 162, conductor 194, probe 166, the liquid in passageway 92, probe 1%, conductor 1%,

junction 111, and terminal 146 will shunt the seriallyconnected resistor 454 and source 456 to effectively reduce the negative bias on the triode 452 and thereby permit that triode to become conductive. Thereupon, the coil 450 will cause the contacts 154 and 15s toopen and will cause the contacts 158 and 161) to close. At such time, the relationship shown at the top of FIG. 9 will be provided.

When the liquid in the passageway 92 simultaneously engages the probes 1114, 1% and 1118, as shown by FIG. 17, the conductor 1%, the probe 184, the liquid in the passageway 92, the probe 168, the conductor 190, the junction 121, and the conductor 192 will shunt the seriallyconnected resistor 474 and source 476 to effectively reduce the negative bias on the triode 472 :and thereby permit that triode to become conductive. Thereupon, the coil 47% will cause the contacts 182 and 184 to. open and will cause the contacts 186 and 188 to close. At such time, the relationship shown at the top of FIG. 10 will be provided.

When the liquid in the passageway 92 simultaneously engages the probes 102, 164, 106 and 1118, the conductor 198, the probe 1132, the liquid in the passageway 92, the probe 183, the conductor 1%, and the junction 191 will shunt the serially-connected resistor 454 and source 456 to effectively reduce the negative bias on the triode 452 and thereby permit that triode to become conductive. Thereupon, coil 459 will cause the contacts 154 and 156 to open and will cause the contacts 153 and 169 to close. At such time, the relationship shown at the top of FIG. 11 will be provided.

The upper end of the coil 4541 is connected to one end of the high voltage secondary winding of the transformer, not shown, of the electronic relay 132, and the other end of that winding is connected to the cathode of the triode 452. Similarly, the upper end of the coil 470 is connected to one end of the high voltage secondary winding of the transformer, not shown, of the electronic relay 161, and the other end of that winding is connected to the cathode of the triode 472. The voltage source 456 includes a triode that is connected as a diode, the filament winding of the transformer of the electronic relay 132, and a capacitor; and that triode is preferably part of a duotriode of which the triode 451i is a part. Similarly, the voltage source 476 includes a triode that is connected as a diode, the filament winding of the transformer of the electronic relay 161, and a capacitor; and that It-riode is preferably part of a .duotriode of which the triode 471) is a part.

Difierent potentiometers 124, 126 and 128 can he used, but it is preferred to use a one hundred ohm potentiometer as potentiometer 124, to use a fifty ohm potentiometer as potentiometer 126, and to use another fifty ohm potentiometer as potentiometer 128. With such an arrangement, it is possible to attain the desired distribution of ohmic resistance in the various potentiometers and still have the total effective ohmic resistance of those potentiometers equal the hundred and thirty-five ohms in the balancing potentiometer 278 within motor 54.

If the air pressure at the other face of diaphragm 114 is materially greater than the air pressure at the other face of diaphragm 120, the electrically conductive liquid in the inclined passageway 92 can be forced down out of engagement with the probes 1412, 104 and 1%. At such time, the liquid will engage only the probe 168; and the contacts 1'54, 156, 158 and 16d of relay .132 and the contacts 182, 184, 186 and 188 of relay 16 1 will be in the positions shown in FIG. 7. This means that terminal 294 of motor '54 is directly connected to the movable contact of potentiometer 124, but is disconnected from terminal 290 by the normally open contacts 158 and 183 of relays 132 and 161, respectively. The terminal 296 of motor '54 is directly connected to the movable contact of potentiometer 128 and is also connected to the terminal 296 of the motor 54 by the normally closed contacts 156 and 184 of relays 132 and 161, respectively. The terminal 290 of motor 54 is connetced to terminal 296 by contacts 184 and 156 but is disconnected from junction 130 by contacts 166 of relay 132 and is disconnected from the movable contact of potentiometer 126 by the contacts 188 of relay 161.

When the electrically conductive fluid moved out of engagement with the probes 162, 164 and 106, and thereby isolated the probe 168, the resistance bridge including the potentiometers 124, 126 and 128 and the potentiometer 278 of motor 54 became unbalanced, and more current flowed through the coil 262 and less current flowed through the coil 260. The differential in current flow through coils 262 and 266 caused the armature 264 to rotate in the counter clockwise direction and moved the contact 266 into engagement with the fixed contact 270. Thereupon, current from the leads 280 passed through the leads 282 an 283 to energize motor winding 274 and rotated the shaft of motor 54 until the movable contact of potentiometer 278 moved all the way to the left, as shown by FIG. 8, to re-balance the bridge. Thereupon, the centering spring, not shown, on the armature 264 returned the movable contact 266 to its neutral position.

At the time the motor 54 was moving the movable contact of potentiometer 276 to the left, it was also rotating the brackets 58 and 69 and the brackets 68 and 70 in the clockwise direction in FIG. 2. That rotation of brackets 58 and 66 shifted arm 42 from the solid line position to the dotted line position in FIG. 2; and that rotation of brackets 68 and 76 rotated the bracket 78 in the clockwise direction to increase the output voltage of Powerstat 76. The resulting increase in the direct current voltage applied to the magnetic clutch in housing 238 increased the speed of the driven shaft 240 until it substantially equalled the speed of the shaft of motor 234. The overall result of the isolation of probe 108 from the other probes is movement of the guide elements 34 to full out position and maximum speed for the blower.

As long as the pressure differential between the atmospheres at the other faces of diaphragms 114 and 120 holds the electrically conductive liquid out of engagement with the probes 102, 104 and 106, the guide elements 34 will remain in full out position and the blower will operate at maximum speed. However, when the pressure differential between the atmospheres at the other faces of diaphragms 114 and 120 decreases to the point where the electrically conductive liquid can engage the probe 106 as well as the probe 198, the terminals 144 and 146 will be connected together by a circuit extending from terminal 146 past junction 191, through conductor 190, through probe 108, through the electrically conductive liquid, through probe 106, through lead 194, past terminal 162, through normally closed contacts 182, past terminal 166, and through lead 200 to terminal 144. The interconnecting of terminals 144 and 146 causes the relay 132 to open its normally closed contacts 154 and 156 and to close its normally open contacts 158 and 160'.

Thereupon, terminal 294 will continue to be connected directly to the movable contact of potentiometer 124 but will be separated from the terminal 290 solely by the normally open contacts 188 of relay 161. The terminal 296 of motor 54 will continue to be directly connected to the movable contact of potentiometer 128, but will be separated from the terminal 296 by the opening of the normally closed contacts 156 of relay 132. The terminal 296 of the motor 54 will be additionally separated from the movable contact or" potentiometer 126 by the now-open contacts 154 of relay 132, but will be connected to junction 13% by the now-closed contacts 160 of relay 132. The result of interconnecting the terminals 144 and 146 of relay 132 is to provide the relationship shown at the top of FIG. 9, and thereby increase the amount of current flowing through the coil 260 while decreasing the amount of current flowing through the coil 262. Thereupon, the armature 264 of the balancing relay will rotate in the clockwise direction to place the movable contact 266 in engagement with the fixed contact 263; and current will then flow through the motor winding 272 and rotate the shaft of motor 54 in the counter clockwise direction. That rotation will continue until the movable contact of potentiometer 27 8 reaches the position shown at the bottom of FIG. 9; and during that rotation the brackets 58 and 60 will move the guide elements 34 to a half out position, and the brackets 68 and 70 will rotate the bracket 78 on the shaft of Powerstat '76 to decrease the voltage applied to the full wave rectifier 232 and thereby reduce the speed of the blower. The blower will preferably rotate at a speed approximately half Way between a pre-set maximum speed and a pre-set minimum speed. The guide elements 34 will remain in half out position and the blower will continue to operate at half speed as long as the electrically con ductive liquid engages just the probes 106 and 108.

If the pressure differential between the atmospheres at the other faces of the diaphragms 114 and becomes even smaller, the electrically conductive liquid will rise to its normal position where one end thereof is between the probes 164 and 102. The resulting circuit which extends from terminal 174 of relay 161 through conductor 192, past junction 121, through conductor 190, past probe 168, through the electrically conductive liquid, through the probe 104, and through lead 196 to terminal 172 of relay 161 will bridge terminals 172 and 174; thereupon causing the normally open contacts 186 and 188 of relay 161 to close, and causing the normally closed contacts 182 and 184 of that relay to open. At such time, the probes 106 and 108 will be connected together but the terminals 144 and 146 of relay 132 will not be connected together because the contacts 182 of relay 161 will be open and will isolate those terminals from each other.

The terminal 294 of motor 54 will be connected directly to the movable contact of potentiometer 124 but will be separated from the terminal 290 by the open contacts 158 of relay 132. Terminal 296 of motor 54 will again be directly connected to the movable contact of potentiometer 128 but will be disconnected from the terminal 290 by the open contacts 184 of relay 161. The terminal 290 of motor 54 will be disconnected from junction by open contacts of relay 132 but will be connected to the movable contact of potentiometer 126 by the closing of the normally open contacts 186 of relay 161. As a result, the relationship shown at the top of FIG. 10 is established; and once again more current will flow through the coil 260 and less current will flow through the coil 262, thereby causing the armature 264 to rotate in the clockwise direction again. The resulting completion of the circuit for the motor winding 272, at contacts 266 and 268, causes the motor 54 to rotate still further in the counter clockwise direction. That rotation will continue until the movable contact of potentiometer 278 assumes the position shown at the bottom of FIG. 10; and during that rotation the brackets 53 and 60 will shift the guide members 34 to their substantially vertical position, and brackets 68 and 70 will shift the bracket 78 to cause Powerstat 76 to supply even less voltage to the full wave rectifier 232. The mag netic' clutch within the housing 238 will thereupon permit the output shaft 246 to rotate at its lowest speed.

The guide members 34 will remain in their substantially vertical position and the blower will continue to run at its lowest speed as long as the pressure differential between the atmospheres at the other faces of the diaphragms 114 and 126 is small. However, if the pressure at the other face of diaphragm 120 appreciably exceeds that at the other face of diaphragm 114, the electrically conductive liquid will rise far enough in the passageway 92 to engage the probe 102. At this time, the probes 108 and 4 will continue to hold the relay 161 energized through the circuit that extends from terminal 174 through lead 192, past junction 191, through lead 190, past probe 188, through the electrically conductive liquid, past probe 104 and through lead 196 to terminal 172. The probes 108 and'ldd will be unable to energize the relay 132 because the circuit through those probes and through the terminals 144 and 146 is broken at contacts 182 of relay 161. However, probes 108 and 182 will energize relay 132 by interconnecting terminals 144 and 146 through a circuit that extends from terminal 146, past junction 191, through lead 190, past probe 108, through the electrically conductive liquid, past probe 102 and through lead 198 to terminal 144. Consequently, the relay 161 will remain in shifted position and the relay 132 will become energized and shift its position.

Thereupon, the terminal 294 of motor 54 will be directly connected to the movable contact of potentiometer 124 and will also be connected to terminal 290 through the now-closed contacts 158 .and 188 of relays 132 and 161, respectively. Terminal 296 will be directly connected to the movable contact of potentiometer 128 but will be disconnected from terminal 290 by contacts 156 and 184 of relays 132 and 161, respectively. Terminal 290 is disconnected from junction 130 by contacts 184 of relay 161, and is disconnected from the movable contact of potentiometer 126 by contacts 154 of relay 132. The result of the conjoint energization of relays 132 and 161 is the relationship shown at the top of FIG. 11; and thereupon the coil 260 will again carry more current and the coil 262 Will carry less current, causing armature 264 to again rotate in the clockwise =di rection and close contacts 266 and 268. The resulting energization of motor winding 2-72 will rotate the shaft of motor 54 until the movable contact of potentiometer 278 reaches the position shown at the bottom of FIG. 11; and during that rotation, brackets 58 and 60 will move the guide members 34 to their in position, and the brackets 68 and 70 will cause the bracket 78 to start moving in the clockwise direction and thereby increase the voltage supplied to the magnetic clutch. This means that as the guide members 34 move from their generally vertical position to their in position the Powerstat 76 increases its output voltage position and thereby increases the speed of the output shaft 240*. The overall result is that when the guide members 34 are in, the blower is operating at a speed approximately the speed of the blower at the half out position of those guide members.

The bracket 78 was able to stop rotating in the counter clockwise direction and to start rotating in the clockwise direction While the bracket 70 was rotating steadily in the counter clockwise direction because the distance between the clamp 74 and the shaft of motor 54 is greater than the distance between the clamp 83 and the shaft of Powerstat 76, and also because the bracket 78 is not permitted to reach the line defined by the shafts of motor 54 and Powerstat 76. This arrangement makes it possible to reduce and then increase the blower speed as the guide members 34 are shifted from their full out position through their half out and vertical positions to their in position.

The guide members 34 will remain in their in position, and the blower will operate at its intermediate speed, as long as the pressure at the other face of diaphragm 120 is sufficiently strong to hold the electrically conductive liquid in engagement with the probe 182. When that pressure becomes equal to or appreciably less than the pressure at the other face of diaphragm 120; the inclination of the guide members 34 and the speed of the blower will be changed. To simplify the explanation of the operation of the first embodiment of control mechanism provided by the'present invention, the changes in the inclination of the guide members 34 and the changes in the speed of the blower have been considered to be due to a continuous and progressive decrease in the pressure at the other face of diaphragm 11-4. However, the said embodiment of control mechanism provided by the present invention does not have to pass through a full cycle before it can move to any desired position. Instead, the said embodiment moves the guide members 34 directly to the desired position and the speed of the blower is also changed directly and immediately.

The extent to which the guide members 34 are moved by motor 54is controlled by adjusting the etfective lengths of the moment arms of brackets 70 and 78', as by setting the clamps 74 and 83 closer to or farther away from the shafts of motor 54 and Powerstat 76. It has been found desirable to adjust the lengths of the moment arms provided by the brackets 70 and 78 so rotation of motor 54 through one hundred and sixty degrees will cause the guide members 34 to rotate fortyfive degrees. Further, it has been found desirable to have the in position of guide members 34 approximately fifteen degrees inwardly of the generally vertical position of those guide members, to have the half out position of the guide members about fifteen degrees outwardly of the generally vertical position, and to have the full out position of the guide members. about fifteen degrees outwardly of the half out position. In setting the effective lengths of the moment arms of the brackets 78 and 78, the moment arm of the former Will, :as explained above, be made longer than that of the latter.

Where individual potentiometers such as 124, 126 and 128 are to be used, those potentiorneters should each have a two watt rating. Such a rating avoiding overheating and the problems consequent thereupon. Where a multitapped, wire-wound resistor is substituted for the individual potentiometers 124, 126 and 128, it should have a six watt rating.

To adjust the potentiometers 124, 126 and 128, or to adjust the various taps on a multi-tapped Wire-wound resistor, the control mechanism should be disconnected from line voltage, and an ohmmeter should be connected to the leads 21-6 and 221. Thereupon, the armature of relay 132 should be shifted and then held in shifted position while the movable contact of potentiometer 124 or a corresponding resistor tap is adjusted to provide a reading of thirty ohms. Once this has been done, the armature of relay 132 should be released and the armature of the relay 161 should be shifted and held in shifted position until the movable contact of potentiometer 126 or corresponding resistor tap is adjusted to provide a reading of sixty ohms. Finally, the armatures of both relays should be shifted and held in shifted position until the movable contact of potentiometer 128 or a corresponding resistor tap is set to provide a reading of one hundred and thirtyfive ohms.

This procedure provides a good initial adjustment of the vertical, half out, full out and in positions of the guide members 34 to secure the precise final adjustment of the various positions of the guide members 34, the ohmmeter is disconnected, the power is reconnected, and the armature of relay 161 is shifted and then held in shifted position. The motor 54 will shift the guide members 34 to their vertical position, and that position can be adjusted by adjusting the position of the movable contact of potentiometer 126 or of a corresponding resistor tap. The half out position is checked and adjusted by permitting the armature of relay 161 to return to normal position and shifting the armature of relay 132, and subsequently adjusting the movable contact of potentiometer 128 or of a corresponding resistor tap. These adjustments in the settings of the movable contacts of potentiometers 126 and 128 will change the total resistance between leads 216 and 221; and hence the power will again be disconnected and the initial adjusting proacsacoa cedure with the ohmmeter will be repeated. These two adjusting procedures are alternated until the precise settings are attained.

In setting the substantially vertical position of the guide elements 34, it is desirable to set those guide elements to provide a slight outward air spillage at the floor level. Such spillage has the effect ofcutting away part of the outermost air Wall of the air screen, and such a cutting away is desirable because that outermost air wall is the wall which entrains most of the dust, dirt and humidity of the outside air. Consequently, it is not desirable to recirculate all of the air of that air wall. The pressure differentials to which the electrically conductive liquid responds, and the resulting inclinations of the guide members 34 and the resulting speed of the blower are suchthat some outward spillage of air will occur at the floor level in each of the moved positions of the guide members 34. The requisite inclination of the guide members 34 to provide outward spillage when those guide members are in their vertical position is easily attained by properly setting the clamps 69 and 47 relative to the connecting rod 66.

The embodiment shown in FIGS. 1-11 provides four discrete and separate positions for the guide members 34, and provides appropriate speeds for the blower. The blower speed varies automatically with the position of the guide members 34, and the blower speed is kept as low as possible. Hence, the said embodiment provides an adequate and pleasing, but not a disturbing, flow of air when the guide members are in their vertical position, and increases that flow only as much as is necessary to prevent breakthroughs in the air screen.

To attain the desired air velocity when the guide members 34 are in their vertical position and to attain the desired increased velocity when those guide members are in their full out position, it is necessary to pro-set the desired maximum output voltage of Powerstat 76, to preset the desired minimum output voltage, and to pre-set the number of degrees through which the bracket 78 must move to reduce the voltage from the maximum value to the minimum value. The pro-setting operations are easily performed by loosening the set screw of bracket 78, inserting the blade of a screw driver in the slotted end of the shaft of Powerstat, rotating that shaft until the desired air velocity is attained, and then marking that position of the shaft. Thereafter the shaft is rotated until he desired minimum air velocity is attained and that position of the shaft is marked The clamps 83 and 74 can then be moved relative to the slots in the brackets 78 and 70 to cause full rotation of the shaft of motor 54 to provide the desired rotation of the shaft of Powerstat 76; and the bracket 78 set and locked in the proper position on the shaft of that Powerstat.

The control mechanism of FIGS. 1-11 can also be controlled by a manually operable potentiometer 222 which is selectively connected to terminals 294 and 296 of motor 54 by the ganged switches 206 and 208. When the movable contact of that potentiometer is set in its extreme clockwise position, the movable contact of potentiometer 278 will be moved to the position shown in FIG. 8 and the guide members 34 will be shifted to their full out position. When movable contact of potentiometer 222 is set in its extreme counter clockwise position, the movable contact of potentiometer 278 will be moved to the position shown at the bottom of FIG. 11 and the guide members 34 will be shifted to their in position. When the movable contact of the potentiometer 222 is set in ny intermediate position, the guide members 34 will be shifted to a corresponding intermediate position. The potentiometer 222 can supply almost an infinite number of manually set positions for the guide members 34.

Referring in FIGS. 12 through 14, the numeral 310 generally denotes a hollow housing; and that housing includes a flanged cup 312 which has two outwardly and downwardly directed feet 314 secured to it. Those feet space the flanged cup 312 from a support 316; and fasteners 31% extend through openings in the feet 314 and seat in openings in that support. A gasket 320 of annular form is supported on the flange of the flanged cup 312; and a thin, flexible diaphragm 322 of resilient and flexible material such as rubber has its outer edge resting upon the gasket 322. The diaphragm 322 has a small central opening. A light-weight stifi plate 324 with a small central opening overlies the center of diaphragm 322, and a similar plate 326 underlies that cener. A light-weight pin 328, which has a small diameter lower end and a still smaller diameter upper end, has its lower end extending through the small openings in plates 324 and 326 and in diaphragm 322. A washer 330 is pressed upon the small diameter lower end of pin 323 and maintains that pin in assembled relation with the plates 324 and 326 and with the diaphragm 322. The diaphragm 322 is large, preferably being six inches or more in diameter, and hence it will have a large area that can be acted upon by a pressure differential.

A small diameter, light-weight plate 332 having a small central opening telescopes down over the smaller diameter upper end of pin 328; and a small diameter, flexible diaphragm 334 having a small central opening also telescopes down over the upper end of pin 328. A second small diameter plate 336 having a small central opening also telescopes down over the upper end of pin 328; and a washer 338 is pressed onto the smaller diameter upper end of pin 323 to maintain the plates 332 and 336 and the diaphragm 334 in assembled relation with pin 328. A spring 340 of spiral configuration underlies the reduced diameter lower end of pin 328 and bears against the bottom of flanged cup 312, thereby biasing the pin 328 upwardly to compensate for the weight of the plates 3'24, 326 332 and 336, for the weight of the center portions of diaphragms 322 and 334, and for the weight of pin 328 and washers 3 3i) and 338.

The upper part of the hollow housing 310 includes a flanged cup 342 which has a sizable opening 346 at the center thereof; and that opening accommodates the small diameter upper end of the pin 328. A gasket 348 of annular configuration underlies the portions of flanged cup 342 which define opening 346 and overlies the outer edge of flexible diaphragm 334. A gasket 350 of annular configuration underlies the outer edge of diaphragm 334; and the gaskets 348 and 350 coact with the diaphragm 334 to render the top of flanged cup 342 air-tight while permitting vertical movement of pin 328 relative to that flanged cup. The flange of the flanged cup 342 overlies a gasket 344 of annular configuration which, in turn, overlies the outer edges of diaphragm 322. Gaskets 344 and 324) coact with diaphragm 322 and flanged cups 312 and 342 to provide an air-tight housing 310 that is divided into two mutually distinct compartments.

A U-shaped bracket 352 is secured to the top of flanged cup 342 by feet 354. An opening 355 is formed in the web of the bracket 352, and that opening is above and in register with the opening 346 in the top of flanged cup 342; and hence the opening 355 accommodates the pin 328 and permits that pin to move freely relative to the bracket 352.

A U-shaped balance arm 358 is rotatably mounted within the U-shaped bracket 352 by a pivot 356 that is fixedly carried by the balance arm 358 and that has pointed ends, not shown, held by jewelled bearings 360. Those jewelled bearings are suitably supported in openings in the upstanding side walls of U-shaped bracket 352.

The balance arm 353 is made of a light-weight metal, and it is provided with openings 364 that reduce the weight of that arm. A threaded rod 366 is secured to the right-hand end of the arm 358, and that threaded rod rotatably supports nuts 368. A cup 370, preferably of plastic material, is secured to the left-hand end of the arm 358; and that cup holds a small quantity of an electrically conductive liquid 372 such as mercury. A layer of oil 374 is provided atop the electrically conductive liquid 372, and that oil is intended to prevent oxidation of the surface of the electrically conductive liquid 372.

The numeral 376 denotes a bridge of insulating material which is suitably secured to the upstanding side walls of the U-shaped bracket 352. That bridge has seven openings through it, and each of those openings has an internally threaded sleeve 378 pressed into it. Seven tungsten-tipped metal screws 380, 382, 384, 386, 388, 398 and 392 have nuts 394 threaded onto their shanks and also have solder lugs 396 telescoped over their shanks. Thereafter the shanks of those screws are threaded into and through the internally threaded sleeves 378. The various screws 388, 382, 384, 386, 388, 398 and 392 are set with the ends thereof at different levels, and the nuts 394 are used to lock those screws in position.

The housing 310 has an opening 338 communicating with one of the two compartments within that housing, and it has an opening 481 communicating with the other compartment within that housing. Those openings are approximately one-eighth of an inch in diameter, and hence while they are large enough to permit prompt movement of the diaphragm 322 in response to changes in pressure differential, they are small enough to prevent too-abrupt and too-sudden movement of that diaphragm. Larger openings could permit too-abrupt movement of the diaphragm and thereby permit some screws to be momentarily immersed when the actual pressure differential would not warrant their immersion. A tube 428 extends from the opening 398 to a hollow housing 422; and a similar tube, not shown, extends from the opening 488 to a second housing, not shown, identical to the housing 422. Both of the housings have spaced sides which are pentagonal in configuration, and each of the housings has a partition 424 extending transversely between the sides thereof. The partition 424 extends close to the inner end of the tube 420 and largely divides the housing 422 into two compartments which communicate with each other adjacent the inner end of the tube 420. A mesh screen 426 of metal extends over the open face of the housing and is supported by the sides and by the partition 424. The mesh screen 426 permits air to pass freely into and out of the two compartments within the housing 422 and thereby enables the tube 428 to place its particular compartments of the air-tight housing 310 in communication with the atmosphere adjacent the housing 422. The housing 422 will be mounted adjacent the outer face of the air screen while the housing connected to the opening 488 in housing 318 is mounted adjacent the inner face of the air screen.

The partition 424 enables the housing 422 to serve as a sensitive pick up of winds from any direction. Also, that partition keeps winds that pass transversely of the axis of the tube 428 from creating a reduced pressure within the housing 422. Hence the partition enables the housing 422 to provide a true indication of the pressure conditions immediately adjacent it.

The numeral 482 denotes a fixed resistor of standard and usual construction, and that resistor will preferably have a resistance of one hundred ohms. The numeral 484 denotes an elongated, wire-wound resistor which has a portion of the insulation thereon scraped away to permit the attachment to the various turns thereof of adjustable taps. The numerals 406, 408, 410 and 412 denote adjustable taps which can be secured to the various turns of the wire-wound resistor 484. That resistor will preferably have a maximum resistance of one hundred and fifty ohms; and one end of that resistor is connected to one end of resistor 482 at junction 416. The other end of resistor 404 is connected to one end of a fifty ohm resistor 413 by a junction 415; and the other end of re sistor 413 is connected to one end of a two hundred ohm potentiometer 414 by a junction 418.

Junction 432 is connected to screw 392 by lead 430, junction 416 to screw 390 by lead 434, tap 486 to screw 388 by lead 436, tap 408 to screw 394 by lead 438, tap 418 to screw 382 by lead 448, tap 412 to screw 380 by lead 442, and junction 418 to screw 386 by lead 428. A lead 446 can extend between junction 432 and terminal 286 of motor 54 in FIG. 7, a lead 448 can extend between junction 418 and terminal 298 of that motor, and a lead 450 can extend between the movable contact of potentiometer 414 and terminal 294 of that motor. Where the leads 446, 448 and 458 are so connected, the control mechanism of FIGS. l4-16 can be substituted for the inclined passageway 92, the relays 132 and 161, and the potentiometers 124, 126 and 128 of FIG. 7.

Before setting the levels of the screws 380, 382, 386, 388, 398 and 392, the balance of arm 358 is adjusted; and that is done by pushing down on the pin 328 to keep that pin from interfering with the movement of the arm 358 and then rotating the nuts 368 until the arm 358 balances nicely. Thereafter both nuts 368 are rotated one half of a turn toward the pivot 356 to provide a slight counter clockwise bias for the arm 358; and that bias will enable the arm 358 to rest upon and follow the pin 328. At this time the pin is permitted to move upwardly and engage the arm 358; the pin 328 and the arm 358 assuming substantially stress-free positions because the tube 428 and its counterpart will have been separated from openings 398 and 484) to permit the pressures at both faces of the diaphragm 322 to be atmospheric pressure. The screw 386 is then rotated until the tip thereof is immersed in the electrically conductive liquid 372 to the depth of one-sixteenth of an inch, and the nut 394 for that screw is tightened to lock that screw in position. With the leads 446, 448 and 450 disconnected from the motor 54, the ohmmeter is connected to leads 446 and 448; and a reading of about three hundred ohms should be obtained. The screw 388, which is connected to the pre-set tap 412, is then rotated downwardly until the ohmmeter drops from three hundred ohms to a lesser preset value, preferably about two hundred and twenty ohms. The screw 388 will then be rotated downward another quarter of a turn and locked by its nut 394.

The screw 382 will be rotated downwardly until the ohmmeter drops from ab out two hundred and twenty ohms to a still lower pre-set reading, preferably about one hundred and ninety ohms. That screw Will then be locked in position by its nut 394. The screw 384 is then rotated downwardly until the ohmmeter drops from one hundred and ninety ohms to a pre-set value, preferably about one hundred and sixty ohms. That screw will then be rotated in the reverse direction for one quarter of a turn to raise it out of contact with the liquid 372, and it will be locked in that position by its nut 394.

The screw 388 is then rotated downwardly until the ohmmeter drops from one hundred and ninety ohms to a pre-set value, preferably about one hundred and thirty ohms. That screw will then be rotated in the reverse direction for one half a turn to raise it out of contact with the liquid 372, and then locked by its nut 394. The screw 3% is then rotated downwardly until the ohmmeter drops from one hundred and ninety ohms to a pre-set value, preferably about one hundred ohms. That screw will then be rotated in the reverse direction for three quarters of a turn to raise it out of contact with the liquid 372, and then locked in position by its nut 394. The screw 332 will be rotated downwardly until the ohmmeter drops to zero; and then that screw will be rotated in the reverse direction one full turn to raise it out of contact with the liquid 372. That screw will be held in that position by tightening its nut 394. Thereafter the ohmmeter is disconnected and is connected to leads 448 and 450. The movable contact of potentiometer 414 is set to provide a reading of approximately one hundred and seventy five ohms; and then the ohmmeter is disconnected, and the leads 446, 448 and 458 are connected to terminals 19 296, 290 and 294, respectively, of motor 54. Also, the tube 420 and its counterpart will be connected to the openings 398 and 430 of housing 310.

If the air pressure at the outer face of the air screen is materially higher than the air pressure at the inner face of that air screen, the diaphragm 322 will move the pin 328 upwardly and rotate the arm 353 until the liquid 372 contacts the screw 392 as well as all the other screws. At this time, the resistors 402, 434 and 413 will be shunted by the electrical conductive liquid 372, and the resistance bridge will consist of potentiometer 278 and the effective portion of potentiometer 414. This means that the resistance bridge is unbalanced, and it will cause the motor 54 to shift the movable contact of potentiometer 278 to a position close to the position shown in FIG. 8. In doing so, that motor will shift the guide elements 34 to their full out position and will rotate the blower at maximum speed.

If the pressure differential between the atmospheres at the opposite faces of the air screen decreases to the point where the arm 358 lowers the cup 370 sufiiciently to expose the screw 392, the resistor 402 will again become an active part of the resistance bridge and will temporarily unbalance that bridge, thereby causing the shaft of motor 54 to rotate in the counter clockwise direction until the bridge is again balanced. During that rotation the guide members 34 will be rotated inwardly from their full out position to a four-fifths out position, and the speed of the blower will be reduced somewhat.

Further decreases in the pressure differential that successively lower container 370 and thereby successively expose screws 390, 388 and 384 will successively cause the three left-hand sections of the resistor 404 to again become active parts of the resistance bridge and temporarily unbalance that bridge. The exposing of those screws thus successively caused the motor 54 to shift the guide members 34 to a three-fifths out position, a two-fifths out position, and a one-fifth out position, and also reduced the blower speed proportionately.

If the pressures at the opposite faces of the air screen approach equality, the screw 382 will become exposed and permit the entire resistor 404 to become an active part of, and thereby temporarily unbalance, the resistance bridge. Thereupon the shaft of motor 54 will rotate to shift the guide members 34 to their vertical position and to cause the Powerstat 76 to operate the blower motor at low speed. At this time, the movable contact of the potentiometer 278 will be in or close to the position shown at the bottom of FIG. 10.

If the air pressure at the inner face of the air screen appreciably exceeds the air pressure at the outer face of that air screen, the container 370 will be moved down far enough to expose the screw 380, thereby leaving only the screw 386 immersed in the liquid 372. At this time, the resistors 402, 404 and 413 will all be active parts of, and Will temporarily unbalance, the resistance bridge. Thereupon the motor '54 will rotate its shaft to re-balance the bridge; and in doing so it will shift the guide members 34 to their in position and will increase the speed of the blower.

To simplify the explanation of the operation of the control mechanism of FIGS. 12-14, it was assumed that a large pressure differential existed initially and that the said pressure differential decreased step by step to zero and that thereafter a reverse pressure differential came into being. However, the control mechanism is not required to pass through a full cycle to respond to a change in the magnitude or nature of the pressure differential. Instead the said control mechanism provides direct and immediate shifting of the guide members 34 when any one of the screws 380, 382, 394, 388, 390 or 392 is immersed or exposed.

Both of the control mechanisms provided by the present invention are versatile and desirable. Moreover, both control mechanisms permit several of the pre-set positions of the guide members to be changed by merely adjusting the movable contacts of potentiometers or by shifting the taps of a wire-wound resistor. Specifically, the shifting of the movable contact of the potentiometer 126 in FIG. 7 can adjust the half out and vertical positions of the guide members 34. Also, the shifting of the taps 466, 403, 418 and 412 can adjust the three-fifths out, the two-fifths out, the one-fifth out and the vertical position of the guide members 34. If any one of those taps is shifted upwardly in FIG. 14, it will cause the pre-set position controlled by that tap to move farther outward and will cause the blower speed corresponding to that tap to increase. Conversely, if any of those taps is moved downwardly it will shift the pre-set posit-ion inwardly and will reduce the corresponding blower speed.

Moreover, by shifting the position of the tap 412 and the position of the movable contact of potentiometer 414, it is possible to change the vertical position to a half in position.

The control mechanism of FIGS. 12-14 has certain advantages over the control mechanism of FIGS. l-ll. For instance, the control mechanism of FIGS. l2-14 is less expensive because it eliminates all need of the electronic relays 132 and 161.. Also, it can provide more pre-set positions for the guide members 34 and more preset speeds for the blower motor. However, the principal advantage which the control mechanism of FIGS. 12-14 has over the control mechanism of FIGS. 1-11 is the promptness with which the former responds to changes in pressure differential. When a pressure differential moves pin 328 upwardly, that pin causes the arm 358 to move the container 370 upwardly an even greater distance; that arm providing a multiplying action. Further, when the container 370 moves downwardly, the mercury 372 therein separates cleanly from the tips of any screws that are exposed during that movement. In contrast, because of the surface tension of aqueous solutions, part of the electrically conductive liquid in the control mechanism of FIGS. l-ll tends to remain in engagement with a probe even after the upper surface of that liquid has moved down below the level of that probe. The overall result is that the control mechanism of FIGS. 12-14 is much quicker and therefore enables the guide members 34 to move more promptly when changes in the pressure differential occur.

The control mechanism of FIGS. 12-14 has still another advantage, namely, its sensitivity can be varied. To increase the sensitivity of the said control mechanism it is only necessary to rotate each of the screws 380, 382, 384, 388, 390 and 392 an additional one-eighth turn in the downward direction. Conversely, to reduce the sensitivity of the said control mechanism, it is only necessary to rotate those screws in the upward direction an eighth of a turn or more.

The control mechanism of FIGS. 12-14 can respond to small changes in the pressure differential. Specifically, the said control mechanism can respond to pressure differentials from minus three-hundredths of an inch water gage to plus five-hundredths of an inch water gage. Further, the said control mechanism unbalances the resistance bridge whenever a change in the pressure differential exceeds approximately eleven-thousandths of an inch water gage.

It is desirable to keep moisture, in the air entering the pick up 422 and its counterpart, from condensing and entering the housing 310. This result is attained by making the tube 420 and its counterpart long enough to provide loops that can entrap and hold any condensed moisture. That moisture can be removed periodically during the periodic checks customarily made of electric motors and the like.

The control mechanisms provided by the present invention are intended for use with air screens, but they can be used with other devices. Specifically, those con-' trol mechanisms could be adapted for use with boiler 21 draft regulators, with building pressure regulators, and with devices that indicate when air filters are to be cleaned or replaced.

Whereas the drawing and accompanying description have shown and described two preferred embodiments of the present invention, it should be apparent to those skilled in the art that various changes may be made in the form of the invention without affecting the scope thereof.

What I claim is:

l. in a control device for a movable component of an air discharge assembly which can be moved to change the deflection of the air of an air screen and for the velocitycontrolling member of said air screen, an electric motor that has a rotatable shaft and that has a potentiometer with a movable contact that is secured to said rotatable shaft and that moves whenever said shaft moves, a tapped resistance that has the taps thereof connectable to spaced points on said potentiometer to constitute a resistance bridge, a variable output transformer that has a control arm and that has its output connected to said velocitycontrolling member, a link means extending between said control arm of said transformer and said shaft of said motor to enable rotation of said shaft to vary the output of said transformer, a second link means that is moved by said shaft of said motor and that is adapted to extend to said movable component of air discharge assembly to move said movable component of said assembiy, and a sensing device that senses changes which if not compensated for could result in undesired deflection of said air screen and that is connected to the taps of said tapped resistor and that selectively passes current through various of the taps of said tapped resistor to unbalance said resistance bridge, said motor responding to the unbalancing of said resistance bridge to rotate its shaft and thereby move said link means, said link means causing said velocity-controlling member to provide high velocity when said movable component of said air discharge assembly is in fully moved position.

2. In a control device for a movable component of an air discharge assembly which can be moved to change the deflection of the air of an air screen, an electric motor that has a rotatable shaft and that has a potentiometer with a movable contact that is secured to said rotatable shaft and that moves whenever said shaft moves, a tapped resistance that has the taps thereof connectable to spaced points on said potentiometer to constitute a resistance bridge, a link means that is moved by said shaft of said motor and that is adapted to extend to said movable component of said air discharge assembly to move said movable component of said assembly, and a sensing device that has a plurality of spaced contacts and an electrically conductive liquid, some of said spaced contacts being adapted to be interconnected by said electrically conductive liquid to unbalance said resistance bridge in one direction, other of said spaced contacts being adapted to be interconnected by said electrically conductive liquid to unbalance said resistance bridge in the opposite direction, said spaced contacts and said electrically conductive liquid being relatively movable in response to changes in pressure at opposite sides of said air screen to selectively interconnect said some spaced contacts by said electrically conductive liquid or to selectively interconnect said other spaced contacts by said electrically con- .ductive liquid, said sensing device responding to increases in pressure at one side of said air screen to interconnect said some spaced contacts by reason of said electrically conductive liquid and thereby unbalance said resistance bridge in said one direction, said sensing device responding to increases in pressure at the opposite side of said air screen to interconnect said other of said spaced contacts by reason of said electrically conductive liquid and thereby unbalance said resistance bridge in said opposite direction, said motor responding to the unbalancing of 22 said resistance bridge to rotate its shaft and thereby move said link means.

3. In a control device, a variable resistor, a plurality of spaced electrically-conductive contacts, a hollow housing, a flexible diaphragm that is disposed Within said housing and that can flex relative to said housing and that divides said housing into two chambers that are isolated from each other but that are responsive to the pressures in each other, a tube that places one of said chambers in communication with the atmosphere at one predetermined place, a second tube that places the other of said chambers in communication with the atmosphere at a secondpredetermined place, a spring that underlies said diaphragm and biases said diaphragm upwardly, a container that is adjacent said housing and that is held in register with said contacts but can move vertically relative to said housing and relative to said contacts, said contacts having the lower ends thereof set at different levels, said container being biased to move downwardly relative to said contacts, said spring and said diaphragm coacting to enable said diaphragm to respond to equal pressures in said chambers and thus in said predetermined places to hold said container in a predetermined vertical position relative to said contacts, said diaphragm responding to increases in pressure at the upper face thereof to flex and thereby permit said container to move downwardly relative to said contacts, said diaphragm responding to increases in pressure at the lower face thereof to flex and thereby force said container to move upwardly relative to said contacts, said contacts being connected to spaced points on said variable resistor, a linkage that extends between said container and said diaphragm and that enables upward flexing of said diaphragm to move said container upwardly relative to said contacts, and an electrically conductive liquid that is held in said container and that is moved relative to said spaced contacts as said container moves vertically, said electrically conductive liquid engaging various of said contacts and thereby varying the effective resistance of said variable resistor as said container moves downwardly and upwardly in response to downward and upward flexing of said diaphragm.

4. In a control device, a variable resistor, a member that has an inclined passage therein, a plurality of spaced, electrically conductive contacts mounted on said member,

each of said contacts having one end thereof extending into said passage, a hollow housing, a second hollow housing, a fiexible diaphragm that is mounted in the first said housing to form two chambers in said housing that are isolated from each other but that are responsive to the pressures in each other, one of said chambers in the first said housing being connectable to one end of said passage, the other of said chambers in the first said housing being connectable to the atmosphere in a predetermined area, a second flexible diaphragm that is mounted in said second housing to form two chambers in said second housing that are isolated from each other but that are responsive to the pressures in each other, one of said chambers in said second housing being connectable to the other end of said passage, the other of said chambers in said second housing being connectable to the atmosphere in a second predetermined area, and an electrically conductive vaporizable liquid that is disposed within said passage and moves upwardly and downwardly in said passage in response to differences between the pressure in said one chamber in the first said housing and the pressure in said one chamber in said second housing, said ends of said contacts being disposed at different levels whereby said electrically conductive vaporizable liquid will engage said ends of said contacts at diiferent times as said electrically conductive vaporizable liquid rises in said passage, said contacts being connected to spaced points on said variable resistor, said contacts responding to rises and falls in said electrically conductive vaporizable liquid to short various portinos of said variable resistor, said flexible diaphrams being thin and readily flexible, the first said diaphragm isolating said electrically conductive vaporizable liquid from the atmosphere in the first said predetermined area while making said one chamber in the first said housing responsive to the pressure in said other chamber in the first said housing and thus responsive to the pressure in the first said predetermined area, said second diaphragm isolating said electrically conductive vaporizable liquid from the atmosphere in said second predetermined area while making said one chamber in said second housing responsive to the pressure in said other chamber in said second housing and thus responsive to the pressure in said second predetermined area.

5. In a control device, a variable resistor, a plurality of spaced, electrically conductive contacts, a hollow housing, a large diameter flexible diaphragm that is mounted in said housing to form two chambers in said housing that are isolated from each other but that are responsive to the pressures in each other, one of said chambers in said housing being connectable to the atmosphere in a predetermined area, the other of said chambers in said housing being connectable to the atmosphere in a second predetermined area, a small light-weight container that is held in register with said contacts but is vertically movable relative to said contacts, said diaphragm supporting the weight of said container, said contacts having the lower ends thereof disposed at different levels, said container being biased to move downwardly relative to said contacts but said disphragm responding to equal pressures at the opposite faces thereof to hold said container in a predetermined vertical position relative to said contacts, said diaphragm responding to increases in pressure at one face thereof the flex and thereby permit said container to move downwardly relative to said contacts, said diaphragm responding to increases in pressure at the opposite face thereof to flex and thereby force said container to move upwardly relative to said contacts, and an electrically conductive liquid in said container, said contacts being connected to said variable resistor, said electrically conductive liquid responding to downward and upward movement of said container to engage various of said contacts and thereby short various portions of said variable resistor to vary the effective resistance of said variable resistor.

6. In a control device, a box-like housing that has one side thereof open and that has an opening in that side thereof which is opposite said open side thereof, a partition that is disposed within said housing and has one end thereof extending toward but terminating short of said opposite side of said housing and has the other end thereof projecting outwardly beyond said open side of said housing, and a perforate cover for said open side of said housing, whereby air that moves laterally of said housing and parallel to said opposite side and that passes through said perforate cover can neither substantially force air into said opening nor draw air from said opening.

7. In a control device, a box-like housing that has one side thereof open and that has an opening in that side thereof which is opposite said open side thereof, a partition that is disposed within said housing and has one end thereof extending toward but terminating short of said opposite side of said housing and has the other end thereof projecting outwardly beyond said open side of said housing, said one end of said partition being in register with said opening in said opposite wall of said housing, and a perforate cover for said open side of said housing, said partition keeping air that moves laterally of said housing and parallel to said opposite side and that passes through said perforate cover from drawing air from said opening.

8. In a control device for a movable component of an air discharge assembly which can be moved to change the deflection of the air of an air screen, an electric motor that has a rotatable shaft, 21 potentiometer with a movable contact that is connected to said shaft and that moves whenever said shaft moves, a tapped resistance that has the taps thereof connectable to spaced points on said potentiometer to constitute a resistance bridge, a link means that is moved by said shaft of said motor and that is adapted to extend to said movable component of said air discharge assembly to move said movable component of said air discharge assembly, and a sensing device that has a plurality of spaced contacts and an electrically conductive liquid and means for holding said electrically conductive liquid adjacent said contacts and for moving said electrically conductive liquid relative to said contacts, said spaced contacts being connected to the taps of said tapped resistance, said sensing device moving said electrically conductive liquid relative to said spaced contacts in response to changes in conditions air pressure at opposite sides of said air screen to selectively interconnect some of said spaced contacts and thereby unbalance said resistance bridge in one direction or to disconnect some of said spaced contacts and thereby unbalance said resistance bridge in the opposite direction, said motor responding to the unbalancing of said re sistance bridge to rotate its shaft and thereby move said link means.

9. A control device that is adapted to provide movement which can be used to move the movable portion of an air discharge assembly of an air screen to change the deflection of the air of said air screen and to move the movable portion of the velocity-controlling member of said air screen to change the velocity of the air of said air screen and that comprises a reversible electric motor, a forward running coil for said motor, a reverse running coil for said motor, an electrically conductive liquid, a pair of contacts that are normally isolated from each other but that can be interconnected by said electrically conductive liquid to energize said forward running coil, a third contact that can coact with said electrically conductive liquid and one of said contacts to pass current to energize said reverse running coil, a link age that is moved by the shaft of said motor and hat is adapted to extend to and to move said movable portion of said air discharge assembly, a second linkage that is moved by said shaft of said motor and that is adapted to extend to and move said movable portion of said velocity-controlling member, and a sensing element that senses changes which if not compensated for could result in undesired deflection of said air screen and that can keep said pair of contacts isolated by keeping said electrically conductive liquid from simultaneously engaging both contacts of said pair of contacts and that can respond to said changes to interconnect said pair of contacts by means of said electrically conductive liquid and thereby energize said forward running coil of said motor, said sensing element responding to relative air pressure changes to cause said third contact and said one contact and said electrically conductive liquid to pass current to energize said reverse running coil.

10. A control device that is adapted to provide movement which can be used to move the movable portion of an air discharge assembly of an air screen to change the deflection of the air of said air screen and that comprises a reversible electric motor, a forward running coil for said motor, a reverse running coil for said motor, an electrically conductive liquid, a pair of contacts that are normally isolated from each other but that can be interconnected by said electrically conductive liquid to energize said forward running coil, a third contact that can coact with said electrically conductive liquid and one of said contacts to pass current to energize said reverse running coil, a linkage that is moved by the shaft of said motor and that is adapted to extend to and move said movable portion of said air discharge assembly, and a sensing element that includes a flexible diaphragm and a housing for said flexible diaphragm, said flexible diaphragm flexing to move said electrically conductive liquid relative to said contacts, one face of said flexible diaphragm being in communication with the atmosphere exteriorly of said air screen, the other face of said flexible diaphragm being in communication with the atmosphere interiorly of said air screen, said flexible diaphragm responding to increase in pressure exteriorly of said air screen to flex in one direction and move said electrically conductive liquid in a predetermined direction and thereby cause said pair of contacts to be interconnected and cause said forward running coil of said motor to be energized, said flexible diaphragm responding to increases in pressure interiorly of said air screen to flex in the opposite direction and provide movement of said electrically conductive liquid in a direction opposite to said predetermined direction and thereby cause said third contact and said one contact of said pair of contacts to pass current to energize said reverse running coil.

11. A control device that is adapted to provide movement which can be used to move the movable portion of an air discharge assembly of an air screen to change the deflection of the air of said air screen and to move the movable portion of the velocity-controlling member of said air screen to vary the velocity of said air in said air screen and that comprises a reversible electric motor, a forward running coil for said motor, a reverse running coil for said motor, a pair of contacts that are normally isolated from each other but that can be interconnected to energize said forward running coil, a third contact that can coact with one of said contacts of said pair of contacts to pass current to energize said reverse running coil, a linkage that is moved by the shaft of said motor and that is adapted to extend to and move said movable portion of said air discharge assembly, a second linkage that is moved by said shaft of said motor and that is adapted to extend to and move said movable portion of said velocity-controlling member, and a sensing element that senses changes which if not compensated for could result in undesired deflection of said air screen and that can keep said pair of contacts isolated and that can respond to said changes to interconnect said pair of contacts and thereby energize said forward running coil 0 fsaid motor, said sensing element responding to air pressure changes of opposite sense to cause said third contact and said one contact of said pair of contacts to pass current to energize said reverse running coil, the first said linkage including a crank arm mounted on said shaft of said motor, said second linkage including a crank on the shaft of said velocity-controlling member, and a connecting rod which extends between said cranks, and means for adjustably mounting said rod along said cranks so as to vary the rates of rotation of said shafts of said motor and of said velocity-controlling member.

References Cited in the file of this patent UNITED STATES PATENTS 874,521 March Dec. 24, 1907 983,179 Swift Jan. 31, 1911 983,877 Cummings Feb. 14, 1911 1,003,882 Culley Sept. 19, 1911 1,078,785 Grossman Nov. 15, 1913 1,568,724 Cox Jan. 5, 1926 2,047,902 Eitzen July 14, 1936 2,327,833 Warner Aug. 24, 1943 2,348,950 Anderson May 16, 1944 2,384,894 Curtis Sept. 18, 1945 2,396,000 Findley Mar. 5, 1946 2,610,565 Stuart Sept. 16, 1952 2,863,373 Steiner Dec, 9, 1958 

1. IN A CONTROL DEVICE FOR A MOVABLE COMPONENT OF AN AIR DISCHARGE ASSEMBLY WHICH CAN BE MOVED TO CHANGE THE DEFLECTION OF THE AIR OF AN AIR SCREEN AND FOR THE VELOCITYCONTROLLING MEMBER OF SAID AIR SCREEN, AN ELECTRIC MOTOR THAT HAS A ROTATABLE SHAFT AND THAT HAS A POTENTIOMETER WITH A MOVABLE CONTACT THAT IS SECURED TO SAID ROTATABLE SHAFT AND THAT MOVES WHENEVER SAID SHAFT MOVES, A TAPPED RESISTANCE THAT HAS THE TAPS THEREOF CONNECTABLE TO SPACED POINTS ON SAID POTENTIOMETER TO CONSTITUTE A RESISTANCE BRIDGE, A VARIABLE OUTPUT TRANSFORMER THAT HAS A CONTROL ARM AND THAT HAS ITS OUTPUT CONNECTED TO SAID VELOCITYCONTROLLING MEMBER, A LINK MEANS EXTENDING BETWEEN SAID CONTROL ARM OF SAID TRANSFORMER AND SAID SHAFT OF SAID MOTOR TO ENABLE ROTATION OF SAID SHAFT TO VARY THE OUTPUT OF SAID TRANSFORMER, A SECOND LINK MEANS THAT IS MOVED BY SAID SHAFT OF SAID MOTOR AND THAT IS ADPATED 